David Furnish was born in Toronto, Ontario, the son of Gladys and Jack Furnish, a director at the Bristol-Myers pharmaceutical company. He has an older brother, John, and a younger brother, Peter. Furnish graduated from the Sir John A. Macdonald Collegiate Institute in 1981 and received a B.A. in Honours Business Administration from the Richard Ivey School of Business at the University of Western Ontario in London, Ontario in 1985.

Furnish began a relationship with singer Elton John in 1993. John proposed to Furnish in May 2005 at a dinner party with friends and family at one of their homes in Old Windsor. Furnish and John entered into a civil partnership on 21 December 2005, the first day that civil partnerships could be performed in England, in the town of Windsor, Berkshire. Their first child, son Zachary Jackson Levon Furnish-John, was born in December 2010 in California via surrogacy. In January 2013, the couple’s second son, Elijah Joseph Daniel Furnish-John, was born through the same surrogate. After same-sex marriage became legal in England and Wales in March 2014, John and Furnish retroactively converted their civil partnership into a marriage and marked the occasion with a ceremony in Windsor, Berkshire, on 21 December 2014, the ninth anniversary of their civil partnership.

In 2015, he was named one of GQ’s 50 best dressed men in Britain.

In June 2019, to mark the 50th anniversary of the Stonewall riots, Queerty named him, along with John, as one of the Pride50 “trailblazing individuals who actively ensure society remains moving towards equality, acceptance and dignity for all queer people”.